1. Field of the Invention
This invention relates to a method for manufacturing an amino-aldehyde solid condensation product. More particularly, this invention relates to a method for manufacturing an amino-aldehyde condensation product wherein a liquid amino-aldehyde precondensate or liquid reactant mixture is introduced into the bottom of a pool of diluent liquid in which solid condensation product is formed.
2 Description of Related Art
Amino-aldehyde solid condensation products are well known and are put to a variety of uses. In particular, urea-formaldehyde pigments are useful as modifiers of cellulosic such as paper. Large quantities of inorganic pigments such as talc, kaolin, calcium carbonate, zinc sulfide, clay, titanium dioxide, and the like are employed as fillers in the production of paper products. Ordinarily, such inorganic pigments are effective in the preparation of paper products having suitable properties of brightness, opacity, basis weight, softness, smoothness, finish, and ink absorption.
An additive for cellulosic products such as paper must perform the functions of cellulosic products such as paper must perform the functions of an inorganic filler for which it is substituted if it is to gain wide commercial acceptance. Further, to be acceptable to the paper industry, a chemical additive for paper must be one which does not migrate from the base sheet to adjacently held absorbent material. Also, the additive must not cause "blocking", i.e., sticking together of adjacent paper layers when the paper is rolled or stacked sheet upon sheet.
Urea-formaldehyde condensation products are suitable as synthetic additives because they provide the above-described desired characteristics to paper and cellulosic products. Condensation products, also called condensate products because they often are prepared from an amino-aldehyde precondensate solution, result from the reaction of, in this instance, urea and formaldehyde to form the polymeric products. Combination of these monomer molecules with the elimination of water is known as a condensation reaction.
Suitable solid condensation products typically contain area and formaldehyde in a range of relative proportions and may be prepared in accordance with many known methods. Condensation products may be useful in more than one technology. For example, see U.S. Pat. No. 3,981,845, wherein a urea-formaldehyde condensation product is described as suitable both as an additive for paper and a reinforcing filler for rubber.
Typical methods of making urea-formaldehyde condensate products are disclosed in U.S. Pat. No. 3,981,845, 3,909,348, and 4,367,171. Other methods of making urea-formaldehyde resins are known. For example, in preparation method disclosed in U.S. Pat. No. 4,410,685, urea and formaldehyde are first reacted in a very acidic solution (i.e., pH less than about 2.5), then the reaction is completed under basic conditions. Such product typically is utilized as an adhesive or binder for woodcontaining constructions.
Typically, however, known preparation methods have drawbacks that make them less than satisfactory in commercial applications. In many known methods for preparing additives for paper, such as the method described in U.S. Pat. No. 3,981,845, a mixture of urea and formaldehyde or a urea-formaldehyde precondensate is polymerized.
In accordance with known methods for manufacturing aminoaldehyde solid condensation products, a liquid precondensate or a liquid mixture of reactants (amino and aldehyde reactants) is added to a liquid diluent pool in a vessel by "top-feeding," That is, the liquid precondensate or liquid reactant mixture is added in or at the upper surface or the pool of diluent liquid in the reaction vessel. The diluent is an aqueous liquid and may be acidic or basic, depending upon the characteristics desired in the solid condensate product. The diluent liquid also may contain catalyst.
Applicant has observed that when liquid precondensate or a liquid reactant mixture is "top-fed" into a well-mixed reactor, the pre condensate or reactant mixture rapidly mixes with the aqueous diluent and is quickly dispersed or diluted in the pool of liquid diluent. This occurs because the liquid pre-condensate or liquid reactant mixture has a density greater than the density of a suitable diluent liquid. Due to its higher density, the feed liquid quickly enters areas of the reaction vessel which are well-mixed and is rapidly mixed throughout the reaction vessel. Under conditions of adequate mixing in the top-fed arrangement, the local concentration of precondensate or liquid reactants never exceeds the final (steady-state) concentration of precondensate or liquid reactants in the reactor. Consequently, the rate of reaction, which varies directly with the reactant concentration in the liquid phase, i.e., it decreases as the concentration of precondensate or reactant mixture in the diluent decreases, is initially at its lowest value.